Sacrococcygeal Teratoma: Understanding Your Pathology Report

Section Editor: Anthea Girdwood MD FRCPC
September 13, 2026

A sacrococcygeal teratoma is a growth made of several different kinds of tissue that develops at the base of the spine, in the area of the tailbone. It is the most common tumor found in newborn babies, affecting roughly 1 in every 35,000 to 40,000 births. It occurs about three to four times more often in girls than in boys.

This article is written for parents and caregivers. Most sacrococcygeal teratomas are not cancer, and most babies who have one do well after surgery. The pathology report matters because it describes three things that shape what happens next. What kinds of tissue the growth contained, whether any part of it was cancer, and whether the whole thing was removed.

Where does a sacrococcygeal teratoma come from?

A teratoma grows from germ cells, the cells that would normally develop into eggs or sperm. Early in development, these cells travel through the body to reach their final position, and a small number can be left behind along the way. The base of the spine is the commonest place for that to happen, which is why this is the commonest site for a teratoma in a baby.

Because germ cells can become any tissue in the body, a teratoma can contain almost anything. Reports often describe skin, hair, fat, cartilage, bone, nerve tissue, glands, and pieces of intestine or airway lining, all within the same growth. Finding this mixture is normal for a teratoma and does not mean something has gone wrong.

Sacrococcygeal teratomas happen by chance during fetal development. They are not caused by anything a parent did or did not do during pregnancy, and in almost all cases they are not inherited.

How is a sacrococcygeal teratoma found?

Many are seen on a routine prenatal ultrasound, often in the second trimester. Others are obvious at birth as a mass at the base of the spine, sometimes a large one. A smaller number sit entirely inside the pelvis and are not visible from the outside. These are found later, when a child is examined for constipation, difficulty passing urine, or a lump felt during a routine check.

If the growth is found before birth, a center for fetal medicine and pediatric surgery closely monitors the pregnancy. A large teratoma has a rich blood supply and can put strain on the baby’s heart. Clinicians monitor its size and blood flow, and plan the timing and method of delivery around it.

The Altman types

Clinicians describe sacrococcygeal teratomas using a system called the Altman classification. It records how much of the growth is outside the body and how much is inside the pelvis or abdomen. This is determined from examination and imaging rather than the pathology report, but it appears throughout your child’s records.

Type I. Almost entirely outside the body, with little or nothing inside the pelvis. The commonest type and the most straightforward to remove.
Type II. Mostly outside, with a significant portion extending into the pelvis.
Type III. Visible from outside, but the greater part lies inside the pelvis and abdomen.
Type IV. Entirely inside, with nothing visible from outside. These are usually found later in infancy or childhood rather than at birth.

The type matters for the operation and for the risk of the growth coming back. Types II and III have a higher chance of recurrence, and type IV is most often diagnosed late.

What the pathologist looks for

After removing the growth, a pathologist examines it. Because a teratoma can contain many mixed tissue types, it must be sampled extensively rather than in one or two places. Larger growths may need dozens of samples.

The examination answers three questions. What tissues are present, and are any of them immature? Is there any area of cancer, which in this setting is almost always a type called yolk sac tumor? Was the growth completely removed, as assessed at the margins (the edges of tissue cut by the surgeon)?

Thorough sampling matters because a small area of cancer within an otherwise ordinary teratoma changes the treatment plan entirely. You can miss such an area if you examine the growth in only a few places.

Mature, immature, and malignant components

The report will describe the growth as one of the following, and this is the most important part

Mature teratoma. All of the tissue is fully developed and looks like normal adult tissue, just in the wrong place. This is not cancer. It is the most common finding in a newborn and is treated with surgery alone.
Immature teratoma. Some of the tissue has not fully developed, most often nerve tissue that resembles the brain of a developing baby. A grade from 1 to 3 describes how much immature tissue is present. An immature teratoma is still not cancer in a newborn, and most are treated with surgery alone, but it carries a somewhat higher chance of coming back.
Malignant germ cell component. An area of true cancer within the teratoma, almost always a yolk sac tumor. This is uncommon in a newborn and changes the treatment, because chemotherapy is added to surgery.

One point is worth understanding clearly, because it explains a great deal about how these growths are managed. The chance of finding cancer rises steeply with the age at which the growth is removed. A large international study followed more than 3,000 children. Cancer was present in roughly 3 percent of growths removed at 3 months of age and 5 percent at 6 months. The figure rose to 10 percent at 1 year and 33 percent at 2 years. This is why surgery is done early rather than watched, and why a growth found late is approached more cautiously.

Why the coccyx is removed

The operation removes the coccyx, or tailbone, along with the teratoma. Parents are often surprised and assume this means the growth invaded the bone. It usually has not.

This is because the cells a teratoma grows from sit at the tip of the coccyx. Leaving the coccyx behind leaves those cells behind, and the growth can return. Removing it is standard practice everywhere and does not mean the situation is worse than expected.

Your child’s report may describe the coccyx as part of the specimen, and may note whether a tumor was present within it. Children do not need a coccyx, and its removal causes no long-term problems with sitting or movement.

Alpha-fetoprotein and why age matters

Alpha-fetoprotein, usually written AFP, is a protein made by the liver and yolk sac of a developing baby. Doctors measure it in the blood before and after surgery, and a rise afterward is often the first sign that a growth has come back.

Reading the number requires care in a baby. Healthy newborns have very high AFP levels, which fall steadily over the first months of life and reach adult levels at around 8 months. A number that would be alarming in a toddler can be entirely normal in a 6-week-old. The level is therefore compared against a range for the baby’s age, and the trend over several measurements matters more than any single result.

Currarino syndrome

A small number of children with a teratoma at the base of the spine have an inherited condition called Currarino syndrome. It combines three features. There is a growth or other mass in front of the sacrum, together with a malformation of the anus or rectum. The third feature is a characteristic notch in the sacral bone, visible on an X-ray.

It is worth knowing about for two reasons. The condition is inherited, usually from a parent who may have mild features and not know it. A diagnosis therefore has implications for the wider family, and genetic testing is offered. And teratomas associated with Currarino syndrome carry a substantially lower risk of containing cancer than isolated sacrococcygeal teratomas do.

If your child’s teratoma was entirely internal, or there are also problems with the anus or rectum, it is reasonable to ask whether Currarino syndrome has been considered.

What is the prognosis?

The outlook for a baby with a sacrococcygeal teratoma is good. Overall survival is above 80 percent across all types, and for the mature teratomas that make up most cases in newborns, it approaches 100 percent.

Mature teratoma. Excellent. Surgery alone is usually curative.
Immature teratoma. Also very good, with reported survival above 90 percent. Follow-up is closer because of a higher chance of recurrence.
With a malignant component. Less favorable but still good, with reported survival approaching 90 percent, because yolk sac tumor responds well to chemotherapy.

The growth comes back in roughly 1 in 10 children, usually within the first two years and most often around 11 months after surgery. About a third of those recurrences contain cancer even when the original growth did not, which is the single most important reason follow-up continues for years rather than months. A higher risk of recurrence is associated with Altman type II or III, with immature histology, and most strongly with a malignant component in the original growth.

The greatest risks occur before and around birth, because of the size of the growth and the strain it can place on the baby’s heart. Once a baby has successfully undergone surgery, the outlook is generally very good.

What happens after surgery?

Most children need no treatment beyond the operation. Where a malignant component was found, chemotherapy follows, and the combinations used for germ cell tumors are highly effective.

Follow-up surprises families because it continues long after the child seems entirely well. It combines physical examination, including a rectal exam to feel for a mass that would not be visible, with AFP blood tests and sometimes imaging. Most centers follow children for at least three years and often longer, because recurrences can carry cancer even when the original growth did not.

Longer-term follow-up also covers bowel and bladder function. A large teratoma, particularly one that extended into the pelvis, can affect the nerves and muscles in that area. Problems with constipation, soiling, or bladder control can emerge as a child grows.

Questions to ask your doctor

What did the pathology report say the growth was made of?
Was it a mature teratoma, an immature teratoma, or was any cancer found?
If it was immature, what grade was given, and what does that mean?
Which Altman type was my child’s teratoma?
Was the whole growth removed, and were the margins clear?
Was the coccyx removed with it?
Was my child’s AFP level compared against the normal range for their age?
How often will AFP be checked, and for how long?
What follow-up examinations and imaging will my child need?
Does my child need chemotherapy, and why or why not?
Should we consider Currarino syndrome, and should our family be tested?
What should I watch for at home that would mean the growth has come back?
Could this affect my child’s bowel or bladder function as they grow?